When a secondary battery such as a lithium-ion battery has been continuously discharged with a large current, the internal resistance value is bound to temporarily rise in much the same way or to an even higher level as the value rises when the battery becomes degraded, and under such circumstances, the battery can no longer perform at its full performance level. PTL1 discloses a battery control method devised to prevent such deterioration in the performance level, whereby an evaluation value, indicating the extent of battery degradation due to continuous battery discharge, is integrated and a restriction is imposed with regard to battery discharge if the integral value exceeds a predetermined allowable value.